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LCD Overview

Monitors have come a long way since they were coupled with computers in the 1970’s. IBM introduced their first color monitor back in 1981; it could render 4 colors with a maximum resolution of 320 x 200. The next progression was EGA, which allowed up to 16 colors back in 1984. From there we had VGA, UVGA, and the still popular UXGA which can support resolutions of up to 1600 x 1200, and over 16 millions colors. Another big leap in technology was the introduction of multi-scan monitors, which gave the end user the ability to change resolutions and frequencies on the fly. Traditional monitors used analog displays, which meant the digital signal coming from the graphics card had to be translated to an analog signal in order for the monitor to work. This technology also takes up more space, due to the fact that the picture is “beamed” onto the screen. In order for the beam to fully extend, it needs to be a certain distance from the display. A good example of this would be a projector. The further the projector is positioned from the wall, the larger the picture. 

LCD technology started back in 1888, invented by an Austrian called Friedrich Reinitzer. He melted cholesteryl benzoate, and let it cool. Upon cooling, he noticed that the liquid turned blue before finally crystallizing. The then crude discovery had no use as of yet, up until RCA made the first experimental LCD back in 1968.

One advantage of using LCD technology is the fact that the signal always stays digital, which means the signal is cleaner. Power consumption is also drastically lower. While the typical CRT monitor consumes 110 watts, LCD monitors consume 30-40 watts on average. The monitor can be sometimes the largest consumption device of a computer workstation, and typically attributes to 80% usage of the systems electricity. Not to sound repetitive, but the size reduction is probably the biggest draw. Because we no longer need the light beam, monitor size can be dramatically smaller.

The term LCD refers to liquid crystal display. An LCD contains tiny liquid crystals, and there are several different types. These crystals react to changes in voltage, and twist according. Depending on the angle, they allow light emitted from behind them to surface. The crystals do not have the ability to create the light themselves, so computer monitors have built in florescent tubes located in different areas which direct light beams to the crystals.

There are two types of LCD monitors: Passive Matrix and Active Matrix, the later being the most common type because of speed. Active Matrix displays use TFT’s (thin filmed resistors).  TFT’s are very tiny transistors and capacitors that are switched on and off to achieve different colors. There are rows of these TFT’s on the screen, and each row displays a different color when turned on. There are three colors: Red, Blue, and Green. Remember, it’s the twisting of the crystal that actually allows the light to bypass the crystal and become displayed. By controlling voltage to the crystal, we can control how much we twist it, which is used to adjust its brightness. Most displays have 256 levels of brightness, which means the crystals can be twisted or untwisted into 256 different positions. By doing this, we create what they call a grey scale. The grey scale is used to create all of our different colors and shades we see on the monitor.

Each color has 256 different shades, which means we can make 16.8 million different colors! To do this, we need a large number of transistors. Depending on the size of the screen, a typical LCD monitor uses more than 3 million transistors!  One transistor bites the dust, and WHAM – a bad pixel. This explains why it’s so common, and why most manufacturers allow 5 or so bad pixels before they will even warranty the unit.  You also should be aware that the larger the monitor, the bigger your chance is of having a bad pixel. Take 1280 x 1024 and times that by 3 (the 3 different colors).  You should have gotten 3,932,160, which is a lot of transistors! The numbers are definitely not on the LCD manufacturer’s side. It’s such a problem with larger units that over 30% of the screens are tossed in the factory because of irregularities.



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